Abstract

In aquatic ecosystems, the ecology of macrophytal detritus aggregations has been investigated over a range of temporal scales. Yet, no attempts have been made to minimize the temporal resolution of the analysis, thus neglecting the occurrence of short-term colonization and decay dynamics for these ephemeral patches of high biological activity. The present study was carried out at two sampling sites in Lake Alimini Grande, a brackish lagoon in South-East Italy. The abundance of macroinvertebrate taxa colonizing prepared packs of reed leaf detritus and the ash-free dry mass of the packs were monitored daily for 40 days. Spectral analysis was used to investigate the fine-scale temporal dynamics of invertebrates colonization and leaf pack mass variations. The macrobenthos found on leaf packs was dominated at both sites by few taxa (i.e., the vagile Lekanesphaera monodi, Microdeutopus gryllotalpa, Neanthes caudata and the sessile Balanus sp.), whose general colonization patterns were described by unimodal curves. At a daily temporal resolution Balanus sp. was characterized by random short-term density variations, while vagile taxa showed non-random, highly site- and species-specific fluctuations generally characterized by an oscillation period comprised between 2 and 3 days. In addition, leaf packs were characterized by non-random, short-term mass oscillations, coherent and in phase with L. monodi abundance fluctuations. Our results highlight the occurrence of short-term, non-random density variations of invertebrate colonizers on leaf detritus patches. In addition, they emphasize a previously unexplored, fine-scale linkage between abundance patterns of invertebrate consumers and short-term mass variations of decaying detritus.

Notes

Acknowledgments

We are grateful to Franca Sangiorgio for kindly providing chemical and physical data on the Lake Alimini system. We also thank two anonymous reviewers for constructive comments that greatly improved the manuscript. Funding from EEC grant ENV-CT97-0584 is acknowledged. This paper is dedicated to the memory of Ennio Mancinelli.

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